The present invention relates to electrical starting and operating apparatus for high intensity gaseous discharge lamps and, in part, is considered to be an improvement of our prior apparatus for such lamps presented in U.S. Pat. No. 3,889,152, granted to the applicants June 10, 1975. As is known, high pressure gas vapor lamps, such as the metallic halide or sodium vapor lamps, require starting voltages that are higher than normal operating voltages when the lamp is drawing operating current; on the order of ten times the normal operating voltages in the case of high pressure sodium vapor lamps. To meet the starting and operating voltage requirements for those types of lamps on an economical basis, various electronic circuits have been used in combination with the reactor or transformer type lamp ballast to generate high voltage pulses for starting the lamp, as is represented in the prior art including our prior patent U.S. Pat. No. 3,889,152, to which the reader may make reference, as well as to U.S. Pat. No. 3,407,334 to Attewell; U.S. Pat. No. 3,679,936 to Moerkins; and U.S. Pat. No. 3,374,396 to Bell.
Generally speaking, the circuit in our prior patent relies on the general phenomenon of discharging a charged capacitor through a portion of the transformer or inductor winding, which serves as the ballast, to thereby by transformer-like action with the remaining winding portion generate a high voltage pulse that is applied across the HID lamp. The normal AC voltage across the lamp is monitored and at some phase during an AC half cycle the voltage in the circuit is sufficient to trigger the switching means and thereby quickly discharge the capacitor creating a high voltage pulse at that time. Subsequent to starting, the lamp operates and draws current and the impedances of circuit elements in series with the HID lamp limits the voltage thereacross to the lower operating voltage. This operating voltage is insufficient in level to thereafter trigger the aforementioned pulse generator switching device and generation of further high voltage pulses ceases. For a detailed understanding of the operation of our prior invention and the unique aspects thereof the interested reader should make reference to the description contained in the cited patent.
In practice, our prior invention has proved useful for its intended purpose but has revealed certain phenomena now considered undesirable. Specifically, in some instances the circuits were used with lamps that were inoperative or defective. However, under the principles of operation of our starting apparatus the high voltage generator continued to function. This caused continuing and persistent generation of the high voltage pulses that placed extra electrical stresses on the ballast reactor or transformer winding as well as presented possible radio frequency interference which it is desired to avoid.
The present invention improves upon such types of prior art starting and operating apparatus for HID lamps, including our own, by inhibiting pulse generation when the lamp is defective or inoperative. In general, it appears that this type of problem may have existed previously or at least appears to be generally presented in U.S. Pat. No. 3,699,385, issued Oct. 17, 1972, to Paget, which has been made known to applicants in connection with a related type of circuit. In Paget there is disclosed a time delay switch which inhibits the operation of a certain type of pulse generating portion of a lamp ballast circuit adapted for use with metal halide lamps, a type of lamp in which the sustaining lamp voltage is very important and the peak voltage requirement is below 1,000 volts. A predetermined time after the appearance of the AC line voltage applied to the ballast, the circuit cuts out or inhibits operation irrespective of whether or not the lamp is in fact in the operating condition, although in other respects the pulse generating circuit appears to continue to operate to some degree, even with the lamp in the operated condition, as described in such patent. A similar type of cut-out or inhibiting action circuit appears to be suggested also in U.S. Pat. No. 3,924,155, issued Dec. 2, 1975, designed for fluorescent lamps, which has been made known to us. The present invention generally follows along the same type of circuit operation described and employs a means to terminate operation of the pulse generator, which combination we believe to be invention in its specific respects in providing a reliable and efficient apparatus.
Accordingly, a principal object of our invention is to provide an improved starting and operating apparatus for HID type lamps and to provide an apparatus that avoids placing undue voltage stresses on associated reactors or transformers when the lamp is defective or removed.